Drill

ABSTRACT

A drill of simple construction, using commercially available tips or tips obtained by simply modifying them, well balanced in cutting resistance, and capable of drilling small-diameter holes. 
     A main cutting edge (12) of a center-side cutting edge 1 is situated on a base line VP of a circular cone having its vertex on a point V on a tool central axis OO and a half vertical angle α. An intermediate cutting edge (2) having a length substantially equal to 1/2 of the length of the main cutting edge (12) is arranged on a straight line V&#39;Q&#39;, extending parallel to a base line VQ, which is symmetrical to the base line VP with respect to the tool central axis OO and advanced ahead of the base line VQ for a lip height t mm in the axial direction, so that a straight line connecting the respective middle points of the intermediate cutting edge (2) and the main cutting edge (12) intersect the tool central axis (OO) substantially at right angles. 
     Since the intermediate cutting edge (2) is advanced only by the lip height t mm, a workpiece is cut by the intermediate cutting edge (2), and a portion of the main cutting edge (12) which corresponds to the intermediate cutting edge (2) is not used for cutting work, so that the cutting resistance is well balanced. Tips (20) and (21), which constitute the cutting edges individually, have a simple construction, and can be formed of commercially available tips or tips obtained by simply modifying them.

TECHNICAL FIELD

The present invention relates to a structure of a drill which uses tips.

The present invention can be utilized for every drilling type of work,and in particular, high-efficiency operation for drilling relativelysmall holes.

BACKGROUND ART

Any of the drills using conventional tips has a relatively large outerdiameter in order to maintain the balance of cutting resistance betweena central edge and an outer peripheral edge. Described in U.S. Pat. No.4,586,858 and Published Unexamined Japanese Patent Application No.62-84912, by the inventor hereof, are drills which use tips of specialshapes such that they can drill holes of relatively small diameters, andthus drills which use tips intended for drilling relatively small holeshave been known publicly.

In a drill disclosed in U.S. Pat. No. 4,586,858, however, a plurality oftips are arranged constituting cutting edges, and portions without thetips are provided so that the cutting edges are partially discontinuous,whereby left- and right-hand cutting edges are well balanced in cuttingresistance. In this case, however, the diameter of each work hole can bereduced by only a limited amount. In a drill described as an alternativeembodiment, on the other hand, tips constituting cutting edges arespecially worked so that a portion incapable of cutting work is arrangedat part of the cutting edge, whereby the cutting resistance is wellbalanced. In this case, special processing of the cutting edges entailshigh cost.

Further, in a drill described in Published Unexamined Japanese PatentApplication No. 62-84912, tips constituting cutting edges are alsospecially worked so that a portion incapable of cutting work is arrangedat part of the cutting edge, whereby the cutting resistance is wellbalanced. This drill also entails high cost.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a drill of simpleconstruction using commercially available tips, if possible, orminimally modified versions thereof, and applicable to drilling work forsmall-diameter holes.

In order to achieve the above object, the present invention is arrangedso that a half vertical angle formed between the ridge of a center-sidecutting edge and the center line of a tool is equal to a half verticalangle formed between the ridge of an intermediate cutting edge on theopposite side and the tool center line, a straight line connecting themiddle point of the length of the ridge between the opposite ends of thecenter-side cutting edge and the middle point of the length of the ridgebetween the opposite ends of the intermediate cutting edge extendssubstantially at right angles to the tool center line, the length of theridge between the opposite ends of the center-side cutting edge issubstantially twice that of the ridge between the opposite ends of theintermediate cutting edge, and the ridge of the intermediate cuttingedge has a lip height in the direction of the tool axis, above the levelof the ridge of the center-side cutting edge, the lip height beinggreater than 1/2 of the feed per drill revolution. Preferably, moreover,the center-side cutting edge and the intermediate cutting edge arecomposed individually of tips removably fixed to the body of a drill.Preferably, the tip is formed by uniformly removing the region near eachvertex of an equilateral triangular configuration so that each sideconstitutes a cutting edge. Alternatively, the tip has a rectangularbasic configuration, and is formed by uniformly removing each twocorresponding vertices on each diagonal so that each side constitutes acutting edge. Two tips of different sizes are fixed to the drill body sothat the respective one sides of the tips constitute the center-sidecutting edge and the intermediate cutting edge individually. Whenincreasing the diameter of work holes, tips of the same shape and sizehaving cutting edges are fixed in symmetrical positions outside thecenter-side cutting edge and the intermediate cutting edge individually.

According to another aspect of the present invention, the tip is formedby uniformly removing the region near each vertex of an equilateraltriangular configuration so that each side constitutes a cutting edgeand a nick is provided at the central portion of each side. Two tips ofthe same shape and size are fixed to the drill body so that therespective one sides of the two tips are situated on the ridge of thecenter-side cutting edge, the respective one sides of the two tipsconstituting the center-side cutting edge. Further, a tip having thesame shape and size as the aforesaid tips is fixed to the drill body sothat one side of the tip constitutes the intermediate cutting edge.

According to still another aspect of the present invention, the tip isformed by uniformly removing the regions near each two correspondingvertices on each diagonal of a rectangular configuration so that eachside constitutes a cutting edge, and one of two tips of the same shapeis fixed to the drill body so that a long side of the tip constitutesthe center-side cutting edge. Further, the other tip is fixed to thedrill body so that a short side of the tip constitutes the intermediatecutting edge.

According to a further aspect of the present invention, the tip isformed by uniformly removing the regions near each two correspondingvertices on each diagonal of a rectangular configuration so that eachside constitutes a cutting edge, providing a nick at the central portionof each long side. Two tips of the same shape and size are fixed to thedrill body so that the respective long sides of the two tips aresituated on the ridge of the center-side cutting edge, the respectivelong sides of the two tips constituting the center-side cutting edge.Further, two tips having the same shape and size as the aforesaid tipsare fixed to the drill body so that the respective short sides of thetwo tips are situated on the ridge of the intermediate cutting edge, therespective short sides of the two tips constituting the intermediatecutting edge.

According to the present invention, as described above, the ridge of theintermediate cutting edge has a lip height in the direction of the toolaxis, above the level of the ridge of the center-side cutting edge, thelip height being greater than 1/2 of the feed per drill revolution, sothat part of a portion to be cut originally by the center-side cuttingedge is cut by the intermediate cutting edge, which is 180° ahead of thecenter-side cutting edge, so that the center-side cutting edge will notcut the portion cut by the intermediate cutting edge. Further, thelength of the ridge between the opposite ends of the center-side cuttingedge is substantially twice that of the ridge between the opposite endsof the intermediate cutting edge, so that a high-performance drill canbe obtained enjoying a simple construction and well-balanced cuttingresistance. Since different regions are cut by the center-side cuttingedge and the intermediate cutting edge, an introduction of an errorbetween the left- and right-hand half vertical angles upon the balanceis very small. Thus, a drill better balanced than conventional drillscan be obtained.

Furthermore, the drill of the present invention can be obtained by usingcommercially available tips or tips obtained by simply modifying them.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a front view of a drill end according to a first embodimentof the present invention using one tip having an equilateral triangularbasic configuration as a tip on each side;

FIG. 1(b) is an enlarged view of the drill end portion shown in FIG.1(a);

FIG. 2 is a plan view of the first embodiment;

FIG. 3 is a front view of a drill end according to a second embodimentof the present invention using one tip having a rectangular basicconfiguration as a tip on each side;

FIG. 4 is a plan view of the second embodiment;

FIG. 5 is a front view of a drill end according to a third embodiment ofthe present invention using a combination of tips of the same shape andsize having an equilateral triangular basic configuration;

FIG. 6 is a plan view of the third embodiment;

FIG. 7 is a front view of a drill end according to a fourth embodimentof the present invention using a combination of tips of the same shapeand size having a rectangular basic configuration; and

FIG. 8 is a front view of a drill end according to a fifth embodiment ofthe present invention using additional tips to the arrangement of thefirst embodiment for increasing the diameter of work holes.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1(a), 1(b) and 2, a drill according to a firstembodiment of the present invention is used to drill a work hole (notshown) in a workpiece (not shown), and a distal end of the drill isprovided with a center-side cutting edge 1 (left-hand cutting edge inFIG. 1) and an intermediate cutting edge 2 (right-hand cutting edge inFIG. 1) for cutting the workpiece. A chip breaker and the like are notshown (in other embodiments also). The center-side cutting edge 1 iscomposed of a central cutting edge 11, which extends from a point S on atool central axis OO to a cutting edge end A, and a main cutting edge 12which extends from the end A to an outer end D. The main cutting edge 12is situated on a base line VP of a circular cone having its vertex on apoint V on the tool central axis OO and a half vertical angle α. Theintermediate cutting edge 2 has its two opposite ends individually ontwo intermediate points E and F on a straight line V'Q', extendingparallel to a base line VQ, which is symmetrical to the base line VPwith respect to the tool central axis OO, and advanced t mm ahead of thebase line VQ in the axial direction. In this case, however, the maximumfeed for each revolution of the drill is f mm/rev, and "t" is a littlegreater than "f/2". The value "t" is called an axial lip height(relative cutting edge height in the axial direction). If this value isgreater than 1/2 of the feed per drill revolution, part of a portion tobe cut originally by the center-side cutting edge 1 is cut by theintermediate cutting edge 2, which operates 180° ahead of thecenter-side cutting edge 1, so that the corresponding portion BC of thecenter-side cutting edge 1 (main cutting edge 12) on the opposite sidedoes not effect cutting work.

In this first embodiment, the center-side cutting edge 1 and theintermediate cutting edge 2 are respectively composed of one side ofbasic equilateral triangular tips 20 and 21, and these tips 20 and 21are removably fixed to the body of the drill by means of bolts 40 and41, respectively. As shown in FIG. 1, the main cutting edge 12 islocated on a side LM of a basic equilateral triangle LMN, and the tip 20is formed by removing the region near each vertex of the basicequilateral triangle so that an outside angle γ at the outer end Dbecomes equal to the sum of the half vertical angle α and a relief angleδ in the axial direction of the tool, thereby providing the cutting edgeon each side. Thus, the inside angle at the vertex A is 60°+γ. If thevertical angle of the drill is 118°, or if the half vertical angle α is59°, the axial relief angle δ at the outer end D of the cutting edge is1°, whereas an angle β formed between the tool central axis OO and thecentral cutting edge 11 is 61°. The intermediate cutting edge 2, whichprovides the lip height t exceeding 1/2 of the feed per drillrevolution, should preferably be composed of the tip 21 which is formedby removing the region near each vertex of a basic equilateral triangle,each side of which is longer than 1/2 of LM, in parallel to the oppositeside so that EF=AD/2. A cutting edge is provided on each side of the tip21, such a side being used as the intermediate cutting edge 2.

Thereupon, let us suppose a condition for the drill having theaforementioned cutting edges such that a bending moment on the drillcaused by the cutting resistance is zero.

We have f_(n) =f_(c) /k, where f_(c) (kgf/mm) is a circumferentialcomponent of the cutting resistance for each unit length of s (mm) alongthe cutting edge; f_(n) (kgf/mm) is a cutting resistance componentperpendicular to the cutting edge within a plane containing the toolcentral axis OO and the ridge of the cutting edge; and k is a constant.If a cutting resistance component in the axial direction of the drilland a cutting resistance component in the radial direction are f_(t)(kgf/mm) and f_(r) (kgf/mm), respectively, the cutting resistance for afine length ds (=dr/sin α) of the cutting edge at an optional point(radius r (mm)) on the cutting edge on the base line having the halfvertical angle α may be expressed as follows:

f_(c) ·ds=k·f_(n) ·dr/sin α with respect to the circumferentialdirection,

f_(t) ·ds=f_(n) ·sin α·dr/sin α=f_(n) ·dr with respect to the axialdirection, and

f_(r) ·ds=f_(n) ·cos α·dr/sin α=f_(n) ·cot α·dr with respect to theradial direction. If those points on the main cutting edge 12 whichcorrespond to the opposite ends E and F of the intermediate cutting edge2 are given as B and C respectively, there will be no cutting actionbetween the points B and C.

If bending moments around a horizontal axis OX passing an optional pointO (OS=a) on the tool central axis OO and an axis OY (perpendicular tothe drawing plane of FIG. 1) perpendicular to the tool central axis OOand the horizontal axis are assumed, the condition for the removal ofthe bending moment on the drill can be obtained where bending momentsare respectively given as zero.

The bending moment around the axis OX may be given by ##EQU1## wherea'=a+r_(B) (cot α+cot β).

Since differences in level at the points E and F are respectively small,cutting resistances due to the difference in level are ignored.

If the above integral is executed supposing radii r at the points A, B,C, D, E and F to be r_(A), r_(B), r_(C), r_(D) and r_(E) respectively,we obtain ##EQU2## Since the point D corresponds to the outer end of thedrill, the radius r_(D) is equal to the radius r_(O) of the drill, thatis, r_(D) =r_(O). Rearranging the equation for simplicity with use ofr_(B) ≈r_(E), r_(C) ≈r_(F), and α≈β, we obtain

    a'(r.sub.O -2r.sub.F +2r.sub.E)-r.sub.A.sup.2 cot α-(1/2)(r.sub.O.sup.2 -2r.sub.F.sup.2 +2r.sub.E.sup.2)cot α=0. (1)

Likewise, if the bending moment around the horizontal axis OY is givenas zero, we obtain ##EQU3## Executing this integral, we obtain ##EQU4##In the same manner as aforesaid, we obtain

    a'(r.sub.O -2r.sub.F +2r.sub.E)-r.sub.A.sup.2 cot α-(1/sin 2α)(r.sub.O.sup.2 -2r.sub.F.sup.2 +2r.sub.E.sup.2)=0. (2)

Subtracting the opposite sides of equation (2) from their correspondingsides of equation (1), we obtain

    tan(α/2)·(r.sub.O.sup.2 -2r.sub.F.sup.2 +2r.sub.E.sup.2 =0.

Accordingly, we obtain

    r.sub.O.sup.2 -2r.sub.F.sup.2 +2r.sub.E.sup.2 =0.          (3)

From equation (1) or (2), therefore, we obtain a'(r_(O) -2r_(F)+2r_(E))-cot α·r_(A) ² =0. In order to fulfill this equation regardlessof the values of a' and α, we should be given

    r.sub.O -2r.sub.F +2r.sub.E =0,                            (4)

    r.sub.A =0.                                                (5)

In order to avoid r<0 despite a practical mounting error, r>0 should begiven. Since the value r is small, only a small error is caused evenwhere r>0. If r is small enough, it hardly affects the balance of thecutting resistance even though β≠α. Since the differences in level atthe point E and F serve to cancel the influence of r, errorsattributable to neglect of the differences in level are scanty.

From equation (3) and (4), we obtain

    r.sub.E =r.sub.O /4,

    r.sub.R =3r.sub.O /4.                                      (6)

That is, the bending moment acting on the drill can be removed bymounting the tips 20 and 21 on the drill body in a manner such that astraight line connecting the respective middle points of theintermediate cutting edge 2 and the main cutting edge 12 intersect thetool central axis OO substantially at right angles when the length EF ofthe intermediate cutting edge 2 is made equal to 1/2 of the length AD ofthe main cutting edge 12 of the center-side cutting edge 11 inaccordance with equation (6).

According to this first embodiment, only one tip, that is, one of thetips 20 and 21 is arranged on each side, so that the invention may bealso applied to a drill with a relatively small diameter. If the tip 21of the intermediate cutting edge 2 is so small that the strength of thetip or mounting screws is not large enough, it is replaced with agreater tip in which regions near its vertices are removed wide. In somecases, a square may be used as a basic configuration of the tip 21 forthe intermediate cutting edge.

The following is a description of a drill according to a secondembodiment of the present invention. In the present embodiment, tipswhich constitute a center-side cutting edge and an intermediate cuttingedge have a rectangular basic configuration. Thus, the presentembodiment differs from the first embodiment in tip configuration. Forother basic arrangements, the present embodiment resembles the firstembodiment, so that common reference numerals are used to designatethose elements which are common to the two embodiments, and adescription of these elements is omitted.

Referring to FIGS. 3 and 4, a rectangle having vertices H, I, J and K(and having long sides HI and JK and short sides IJ and KH) is used as abasic configuration of tips 22 and 23 as shown in FIG. 3. With respectto the center-side cutting edge 1, regions near the vertices I (and K)are removed so that an outside angle at an outer end D is equal to thesum (α+δ) of a half vertical angle α and a relief angle δ in the axialdirection of the tool, and regions near the vertex H (and also vertex J)are removed so that an inside angle at a cutting edge end A becomes 2α,forming a central cutting edge 11. For example, α=75° and δ=1° areappropriate practical values. Those portions left after removing therespective opposite ends of the long and short sides are used as cuttingedges. A long-side portion and a short-side portion are used as a maincutting edge 12 (on the left-hand side) and an intermediate cutting edge2 (on the right-hand side), respectively, and the tips 22 and 23 areremovably fixed to the drill body by means of bolts 42 to 45. Therespective widths of the main cutting edge 12 and the intermediatecutting edge are in the ratio of 2:1. In this case, two cutting edges ofeach tip can be used alternately by changing the left- and right-handtips with each other. The tips 22 and 23 of the same shape and size areused according to this second embodiment; however, tips of differentsizes may be used for the center-side and intermediate cutting edges.

The following is a description of a drill according to a thirdembodiment of the present invention. The drill of the present embodimentis one whose cutting edges are formed by combining tips of the sameshape and size having a equilateral triangular basic configuration. Thisdrill differs from the drill of the first embodiment in that acenter-side cutting edge 1 is composed of tips 24 and 25 of the sameshape and size. Referring to FIGS. 5 and 6, the regions near therespective vertices of tips 24, 25 and 26 are uniformly removed so thatan outside angle at each outer end is equal to the sum (α+δ) of a halfvertical angle α and a relief angle δ in the axial direction of thetool, and nicks 3, 4 and 5 are provided individually at the respectivecentral portions of the individual sides so that the cutting edges arearranged on each side. Although nicks generally serve to fractionalizeswarf, the nicks 3 and 4 of this embodiment serve as boundaries betweencutting regions. The tips 24, 25 and 26 have the same shape and size.The two tips 24 and 25, whose cutting edges are situated on the baseline of a circular cone having a half vertical cutting edge angle α, arearranged closely in contact with each other, and are removably fixed tothe drill body by means of bolts 46 and 47 so that a main cutting edge12 is composed of one side of each of the tips 24 and 25. On theopposite side of the tool central axis OO, the single tip 26 isremovably fixed to the drill body by means of a bolt 48 so that anintermediate cutting edge 2 with a required lip height is composed ofone side of the tip 26.

Those cutting edge portions of the tips 24 and 25, which constitute thecenter-side cutting edge 1, extend between the nicks 3 and 4, correspondto the intermediate cutting edge 2, and cutting is effected by means ofthe intermediate cutting edge 2. The cutting edge portions between thenicks 3 and 4 are fixed within a region which is not used in the cuttingwork. With use of this arrangement, influences of the nicks upon thebending moment caused by the cutting resistance are canceled to maintainbalance. The tips 24, 25 and 26, which constitute the cutting edges, maybe replaced with one another so that intact cutting edges are used.Where α+δ=60°, in particular, the tips have a symmetrical configuration,so that the construction is simple and practical.

The following is a description of a drill according to a fourthembodiment of the present invention. The drill of the present embodimentis a drill whose cutting edges are formed by combining tips of the sameshape and size having a rectangular basic configuration. This drilldiffers from the drill of the third embodiment in that the tipconfiguration is rectangular.

Referring to FIG. 7, tips 27, 28, 29 and 30, which are of the same shapeand size, each have a rectangular basic configuration whose long andshort sides have lengths substantially in the ratio of 2:1. When acenter-side cutting edge 1 is composed of the respective long sides ofthe two tips 27 and 28, the outer end portion of each long side isremoved aslant for a fine length m so that the outside angle becomesequal to the sum (α+δ) of a half vertical angle α and a relief angle δin the axial direction of the tool, and the center-side end portion ofeach side is obliquely removed for a fine length n so that the insideangle becomes 2α. Thus, a nick with a width (m+n) is provided in thecentral portion of a main cutting edge. A cutting edge is provided oneach side. In this manner, the tips 27 to 30 are formed having the sameshape and the same size.

The cutting edges on the respective long sides of the tips 27 and 28 aresituated on the base line of a circular cone having a half verticalcutting edge angle α. The tips 27 and 28 are arranged closely in contactwith each other and are removably fixed to the drill body by means ofbolts 49 and 50, whereby the center-side cutting edge is formed. On theopposite side of the tool central axis OO, the tips 29 and 30 arearranged, each extending vertically long, so that their respective shortsides are used as cutting edges and are removably fixed to the drillbody by means of bolts 51 and 52, whereby an intermediate cutting edge 2is formed having a required lip height. The positions of arrangement ofthe tips 29 and 30, which constitute the intermediate cutting edge 2,corresponds to the position between two nicks of the center-side cuttingedge 1. Since the workpiece is cut by means of the intermediate cuttingedge 2, the cutting edge portion between the two nicks of thecenter-side cutting edge 1 is not used for cutting work. Thus, newcutting edges can be obtained by replacing the tips 27 and 28.

The following is a description of a drill according to a fifthembodiment of the present invention. The drill of the present embodimentis obtained by adding tips to the drill of the first embodiment so thata work hole of a larger diameter can be formed. In FIG. 8, as comparedwith the drill of the first embodiment shown in FIG. 1, tips 31 and 32of the same shape and size are removably fixed in symmetrical positionsoutside left-and right-hand cutting edges of the drill by means of bolts53 and 54, respectively, to form cutting edges 6 and 7 with one side ofthe tips 31 and 32, respectively. The cutting edge 6, formed of the tip31 added to a center-side cutting edge 1, is located on the same linewith a main cutting edge of the center-side cutting edge 1, whereas thecutting edge 7, which is formed of the tip 32 added to an intermediatecutting edge 2, is arranged without a lip height t.

Advantages of the present invention will now be enumerated.

(1) Since the lip height is provided for the intermediate cutting edgeso that the portion of the center-side cutting edge corresponding to theintermediate cutting edge does not effect cutting work, the cuttingresistance is well balanced.

(2) Commercially available tips or tips obtained by simply modifyingsuch tips can be used for constituting the cutting edges by simplyproviding the intermediate cutting edge with the lip height, so that alow-cost drill capable of drilling small-diameter holes can be obtained.

(3) Since the individual sides of the tips constitute the cutting edges,the tips can be effectively used by being refixed so that another sideof each tip serves as a new cutting edge of the drill when a cuttingedge on one side of the tip is used up.

What is claimed is:
 1. A drill having a drill body, a tool center lineand a feed per drill revolution, said drill comprising:a first cuttingedge forming a first angle with the tool center line; a second cuttingedge located in a same plane as said first cutting edge and on anopposite side of the tool center line, said second cutting edge forminga second angle with said tool center line equal to said first angle; amiddle point of said first cutting edge and a middle point of saidsecond cutting edge connected by an imaginary straight line extendingsubstantially perpendicular to the tool center line; a length of saidfirst cutting edge being substantially twice a length of said secondcutting edge; and said second cutting edge having a lip height in adirection of the tool center line, above a level of said first cuttingedge, said lip height being greater than 1/2 of the feed per drillrevolution.
 2. The drill according to claim 1, wherein said firstcutting edge and said second cutting edge comprise tips fixed to thedrill body.
 3. The drill according to claim 2, wherein each of said tipsis removably fixed to the drill body.
 4. The drill according to claim 3,wherein said tips comprise:a first tip having a substantiallyequilateral triangular configuration defined by three first tip verticeswith respective regions, uniform in shape near each first tip vertex,removed, each side of said first tip, defined by two of said three firsttip vertices, being a cutting edge, one of said cutting edges of saidfirst tip being said first cutting edge; and a second tip having asubstantially equilateral triangle configuration different in size thansaid first tip and defined by three second tip vertices, with respectiveregions, uniform in shape and near each second tip vertex, removed, eachside of said second tip, defined by two of said three second tipvertices, being a cutting edge, one of said cutting edges of said secondtip being said second cutting edge.
 5. The drill according to claim 3,wherein said tips comprise:first, second and third tips, each tip havinga same size as one another and a substantially equilateral triangularconfiguration defined by three vertices, with respective regions,uniform in shape near each vertex, removed, each side, defined by two ofsaid three vertices, being a cutting edge; each side of said first,second and third tips having a nick formed in a respective centralportion; said first and second tips being situated such that one side ofsaid first tip and one side of said second tip are aligned with oneanother to form said first cutting edge; and said third tip beingsituated such that one side of said third tip is said second cuttingedge.
 6. The drill according to claim 3, wherein said tipscomprise:first and second tips, each tip having a substantiallyrectangular configuration defined by four vertices, with respectiveregions, uniform in shape, near opposite vertices, removed, each sidebeing a cutting edge; and said first tip being fixed to the drill bodysuch that a long side of said first tip is said first cutting edge andsaid second tip is fixed to the drill body such that a short side ofsaid second tip is said second cutting edge.
 7. The drill according toclaim 3, wherein said tips comprise:first through fourth tips, each tiphaving a same size as one another and substantially rectangularconfiguration defined by four vertices, with respective regions, uniformin shape, near opposite vertices, removed, each side being a cuttingedge; each long side of each tip having a nick formed in a respectivecentral portion; said first and second tips being fixed to the drillbody such that first and second long sides of said respective first andsecond tips are aligned with one another to form said first cuttingedge; and said third and fourth tips being fixed to the drill body suchthat first and second short sides of said respective third and fourthtips are aligned with one another to form said second cutting edge. 8.The drill according to claim 4, further comprising:third and fourthtips, each of said third and fourth tips having a same size as oneanother and a substantially equilateral triangular configuration definedby three vertices, with respective regions, uniform in shape near eachvertex, removed, each side, defined by two of said three vertices ofsaid respective third and fourth tips, being a cutting edge; said thirdtip having one cutting edge in line with said first cutting edge; andsaid fourth tip, having one cutting edge parallel to said second cuttingedge and below said level of said second cutting edge in said directionof the tool center line by an amount equal to said lip height,symmetrical with said third tip about the tool center line.